Catalyst for propylene polymerization

ABSTRACT

A catalyst for use in the formation of polypropylene is disclosed that comprises a titanium compound having at least one titanium-halogen bond, supported on an activated, amorphous magnesium dihalide support that is essentially free of alkoxy functionality, with a titanium metal content of no more than about 2 wt %, based on the weight of the support, and an internal donor component. This catalyst is made by a: forming a combination of titanium tetrachloride, magnesium-containing compound that can be converted to magnesium dihalide and internal electron donor in an aromatic hydrocarbon solvent and bringing that combination to elevated temperature to form an intermediate product; washing the intermediate product with an aromatic hydrocarbon solvent at elevated temperature to produce a washed product and a supernatant followed by decantation of the supernatant therefrom; treating the washed product with titanium tetrachloride in an aromatic hydrocarbon solvent to form a treated product and a supernatant followed by heating of the treated product and supernatant, decantation of the supernatant therefrom, and washing of the treated product with an aromatic hydrocarbon solvent at elevated temperature; decantation of the supernatant therefrom, and washing of the treated product with an aromatic hydrocarbon solvent preferably at least one or two more times; and addition of an aliphatic hydrocarbon solvent to the treated product with decantation of the solvent therefrom to form a washed product which can be used as a propylene polymerization catalyst. If desired, after the formation of the washed product resulting from addition of the aliphatic hydrocarbon solvent, mineral oil can be added to the washed product to form a slurry containing the final catalyst.

BACKGROUND OF THE INVENTION

This invention relates to the synthesis of a catalyst for thepolymerization of propylene. This catalyst has high activity, andproduces a polymer product having high stereospecificity and high bulkdensity. The catalyst's activity is long lived and it shows a goodtemperature response. All of these features are desirable for acommercial propylene polymerization catalyst.

SUMMARY OF THE INVENTION

The present invention relates to a process for forming a propylenepolymerization catalyst. This process, in general terms, comprises:forming a combination of titanium tetrachloride, a soluble or insolublemagnesium-containing compound that can be converted to magnesiumdihalide, such as a magnesium chloroalkoxide, and an internal electrondonor, such as phthalate ester, in an aromatic hydrocarbon solvent andbringing that combination to elevated temperature to form anintermediate product which is separated by, for example decantation;washing the intermediate product with an aromatic hydrocarbon solvent atelevated temperature to produce a washed product and a supernatantfollowed by decantation of the supernatant therefrom; treating thewashed product with titanium tetrachloride in an aromatic hydrocarbonsolvent, preferably two or three more times, to form a treated productand a supernatant followed by heating of the treated product andsupernatant, decantation of the supernatant therefrom, and washing ofthe treated product with an aromatic hydrocarbon solvent at elevatedtemperature, as previously described, with separation of the desiredproduct (for example, also by decantation); and addition of an aliphatichydrocarbon solvent to the treated product with decantation of thesolvent therefrom to form a washed product which can be used as apropylene polymerization catalyst, optionally after the addition ofmineral oil to the washed product to form a slurry containing thecatalyst.

The soluble or insoluble magnesium-containing compound that can beconverted to magnesium dihalide can be selected from one or more of thefollowing types of compound: magnesium dialkoxides (e.g., magnesiumdiethoxide); chloromagnesium alkoxides (e.g., chloromagnesium ethoxide);magnesium dihalide electron donor adducts (e.g., MgCl₂(EtOH)_(x) andMgCl₂(THF)_(x), where THF is tetrahydrofuran and x in both cases is≧0.5; alkylmagnesium halides (“Grignards”, such as chlorobutylmagnesium;and dialkylymmagnesium compounds, such as butylethylmagnesium. In allthe foregoing classes of compound, the number of carbon atoms in thealkoxide/alkyl moiety or moieties, as appropriate, will range from oneto about twelve, preferably four. Any of such precursors can besupported on an inert carrier, such as silica.

The internal electron donor can be selected from the known types ofinternal donor including the following classes: the phthalates and theirderivatives; the benzoates and their derivatives; the silanes andsiloxanes; and the polysilanes and polysiloxanes.

In accordance with the present invention, the selected magnesiumdichloride source compound cannot be a magnesium dialkoxide when theselected internal donor is a halo phthaloyl derivative.

The process of this invention produces a polymerization catalyst thatcomprises a titanium compound having at least one titanium-halogen bondthat is supported on an activated, amorphous magnesium dihalide supportthat is essentially free of alkoxy functionality, the titanium metalcontent in the catalyst preferably being no more than about 2 wt %,based on the weight of the support, and an internal donor, such as aphthalate ester donor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the following description focuses upon a certain preferredmagnesium dihalide source material, namely, chloromagnesium ethoxide andinternal donor (diisobutyl phthalate), it is to be understood that thebroader possibilities for the selection of each, just describedhereinabove, can be utilized in place of these two selections.

The catalyst of the present invention is made using a series of multipletreatment cycles, each of which involves the reaction of mixtures oftitanium tetrachloride and an alkylbenzene solvent, such as toluene,with a support precursor followed by treatment of the solid with anaromatic hydrocarbon solvent, which is preferably an alkylbenzenesolvent. Representative aromatic solvents that can be used in theprocess that is described herein include benzene, such haloaromaticsolvents as the chlorobenzenes, and such alkylbenzene solvents astoluene and xylene. These reaction steps are carried out at elevatedtemperature. If a lower boiling solvent of this type, such as benzene,is used it may be necessary to use superatmospheric pressure to get tothe desired temperature conditions. During the first titaniumtetrachloride/aromatic solvent reaction step, an internal phthalateester donor, such as the preferred di-isobutylphthalate, is added. Ifthe ultimate polymer product that is to be produced is to have desirableparticle size and morphology characteristics, an appropriate particlesize and morphology-controlled support precursor needs to be used. Thetreatment cycles then need to be carried out in such a manner as topreserve these features in the final catalyst so that the polymerproduct replicates those features.

The initial step of the process of the present invention involvesforming a combination of titanium tetrachloride, magnesiumchloroalkoxide, for example, and phthalate ester in an aromatic solventand bringing that combination to elevated temperature to form anintermediate product. The preferred magnesium chloroalkoxide willcontain from one to about twelve carbon atoms in the alkyl moietytherein. The most preferred magnesium chloroalkoxide is magnesiumchloroethoxide. Toluene has been found to be a preferred alkylbenzenesolvent for use, with xylene, ethylbenzene, propylbenzene,isopropylbenzene, and trimethylbenzene also being useful. The preferredphthalate ester may contain from one to about twelve carbon atoms in thealkyl groups therein, with representative compounds including dimethylphthalate, diethyl phthalate, di-n-propyl phthalate, di-isopropylphthalate, di-n-butyl phthalate, di-butyl phthalate, di-tert-butylphthalate, diisoamyl phthalate, di-tert-amyl phthalate, di-neopentylphthalate, di-2-ethylhexyl phthalate, and di-2-ethyldecyl phthalate. Thedonor can be added at room temperature to the other components and themixture can then be brought to elevated temperature (for example, atabout 100° C. to about 140° C., preferably from about 110° C. to about120° C.) or it can be added to the other two components either at roomtemperature and heated up to about 100° C. or can be added to thosecomponents after they have been heated to a desired temperature. Theamount of titanium tetrachloride to aromatic solvent will generallyrange from about 40% to 80% on a volume basis and, generally, from aboutthree to about four treatment steps have been found to be adequate. Thevolume of titanium tetrachloride and solvent to grams of supportprecursor that is employed will generally be from about 5 to about 10milliliters of titanium tetrachloride and solvent per gram of supportprecursor. The combination of components is preferably held together forup to about ten hours, preferably from about one to about two hours andis agitated. The intermediate solid product from this initial reactionstep is then recovered after the supernatant is decanted.

The intermediate product from the initial step is then washed with anaromatic hydrocarbon solvent, such as an alkylbenzene solvent (forexample, toluene), at elevated temperature (e.g., from about 100° C. upto the boiling point of the solvent) to produce a washed product and asupernatant phase. The washing can be practiced in up to about threeseparate washing steps. The supernatant in each washing step is decantedfrom the washed product. This washing serves to remove undesirableby-products that contain titanium. The volume of aromatic solvent thatis used per gram of support precursor in this step will generally rangefrom about 5 to about 25 milliliters per gram.

The washed product from the preceding step is then treated with titaniumtetrachloride in an aromatic solvent of the type previously describedunder the previously described conditions to form a treated product anda supernatant. This step converts unreacted alkoxide moieties of thestarting magnesium chloroalkoxide reagent and extracts undesiredtitanium-containing by-products. This combination is then heated (e.g.,at from about 100° C. to about 140° C.) followed by decantation of thesupernatant phase that exist and washing of the treated product with anaromatic hydrocarbon solvent, preferably in a washing cycle of from oneto two step(s) each.

After the desired number of treatment/wash cycles, the product from thepreceding step then has an aliphatic hydrocarbon solvent, such ashexane, added to it with decantation of the resulting supernatant phasetherefrom. Washing of the catalyst with aliphatic solvent (e.g., up toabout 3-8 separate washing steps) serves to remove free titaniumtetrachloride and residual aromatic solvent. This forms a washed productthat can be used as the catalyst.

An optional final step is the addition of mineral oil to the washedproduct from the preceding step to form a mineral oil/catalyst slurrythat can be employed as the propylene polymerization catalyst. Drying ofthis slurry is usually avoided since it can result in a substantialdecrease in catalyst activity (e.g., up to as much as 50%).

The catalyst composition that can be formed from the previouslydescribed process appears to be a novel composition of matter in certainembodiments. It comprises a titanium compound having at least onetitanium-halogen bond that is supported on an activated, amorphousmagnesium dihalide support that is essentially free of alkoxyfunctionality. In its broadest embodiment, the catalyst composition hasthe following physical parameters: weight percent titanium—from about 1%to about 4%; weight percent phthalate ester—from about 10% to about 25%;phthalate ester to titanium molar ratio—from about 0.9 to about 2;weight percent magnesium—from about 14% to about 23%; magnesium totitanium molar ratio—from about 7 to about 30; surface area—from about250 m²/gm to about 500 m²/gm; pore volume—from about 0.2 cc/gm to about0.5 cc/gm; and average pore diameter—no more than about 50 Angstroms.

More preferred embodiments of the catalyst composition have thefollowing physical parameters: weight percent titanium—less than about2.0%, most preferably from about 1% to about 2.5%; weight percentphthalate ester—from about 10% to about 20%; phthalate ester to titaniummolar ratio—from about 1 to about 1.9; weight percent magnesium—fromabout 18% to about 21%; magnesium to titanium molar ratio—from about 14to about 29; surface area—from about 300 m²/gm to about 500 m²/gm; porevolume—from about 0.2 cc/gm to about 0.4 cc/gm; and average porediameter—no more than about 35 Angstroms.

Based on the very high productivity and low titanium (Ti) content of thecatalyst of this invention, the polypropylene product that is formedfrom using that catalyst composition is deemed to be a novel compositionhaving a very low residual Ti concentration. Depending upon thepolymerization time and temperature, polymer with less than about 0.20ppm Ti, preferably less than 0.15 ppm Ti, most preferably less than 0.10ppm Ti can be produced.

The Examples that follow are provided to illustrate certain preferredembodiments of the invention.

EXAMPLE 1

Catalyst Preparation

In a nitrogen filled dry box, 10.0 g of a mixed phase ClMg(OEt) wascharged into a 500 ml 4-neck round bottom flask. The flask was fittedwith a mechanical stirrer, nitrogen inlet adapter, condenser withnitrogen outlet adapter, and septum, and removed from the dry box to aSchlenk line. Then, 30 ml of dry toluene was added, the mixture wasstirred to suspend the solid, and 20 ml of TiCl₄ was added to thestirred slurry at a rate that maintained the temperature ≦25° C. Theslurry was heated to 70° C. and 3.78 g of diisobutylphthalate was added.The mixture was heated to 115° C. and was held at this temperature fortwo hours.

At the end of the reaction, the agitation was stopped and the solidswere allowed to settle. The supernatant was decanted, 200 ml of toluenewas added, the reaction media was heated to just below reflux, and washeld for fifteen minutes at this temperature. The solids were thenallowed to settle and the supernatant was decanted. The toluenetreatment was then repeated.

Then, 30 ml of toluene and 20 ml of TiCl₄ were added, the media washeated to 115° C., and was held for one hour. After allowing the solidsto settle, the liquid was decanted, and the solids were treated twicewith 200 ml of toluene as described above. After these treatments, thesequence of the TiCl₄-toluene reaction and two toluene treatments wasrepeated twice. After the last toluene decant, the solids were washedfive times with 100 ml each of hexane. The catalyst was then isolated asa slurry.

Analysis of the solid catalyst component showed it to contain 21 wt % Mgand 1.5 wt % Ti.

Catalyst Testing

A 4 liter autoclave equipped with an agitator was purged with nitrogenuntil oxygen and water have been reduced to acceptable levels. Then,under a N₂ purge, 50 ml of purified hexane was added to the reactor,followed by 7.0 mmole of TEAL and 0.48 mmole ofdicyclopentyldimethoxy-silane. The catalyst slurry prepared above,containing 4 to 6 mg of the solid catalyst, was added to 45 ml ofpurified hexane and then was added to the reactor. The reactor wasclosed and 2.5 l of purified propylene was added, followed by 3.6 l(STP) of H₂. The contents of the reactor were stirred and were heated to70° C. The reaction mixture was maintained at 70° C. for one or twohours. The reactor was then vented and cooled.

The resulting polymer was collected and dried. The polymer was weighedand an activity, defined as kg polymer/g catalyst charged wascalculated. The polymer poured bulk density (PBD) and total xyleneinsolubles (TXI) were measured. The controlled particle sizedistribution and morphology of the starting support precursor wasmaintained in the polymer particles. The results of these tests wereshown in Table 1. In many cases, 2-3 tests were run on each catalyst andthe average results of these tests were reported.

EXAMPLE 2

A catalyst preparation was carried out using the procedure described inExample 1, except that 25 ml of toluene and 25 ml of TiCl₄ were used inthe reaction steps. Analysis of the solid catalyst component showed itto contain 21 wt % Mg and 1.5 wt % Ti. Testing was carried out asdescribed in Example 1, and the results are shown in Table 1, below.

EXAMPLE 3

A catalyst preparation was carried out using the procedure described inExample 1, except that 20 ml of toluene and 30 ml of TiCl₄ were used inthe reaction steps, and only 1×200 ml toluene treatment was used aftereach TiCl₄/toluene reaction. Analysis of the solid catalyst componentshowed it to contain 19 wt % Mg and 1.8 wt % Ti. Testing was carried outas described in Example 1, and the results are shown in Table 1, below.

EXAMPLE 4

A catalyst preparation was carried out using the procedure described inExample 1, except that the reactor was a 250 ml round bottom flask, 10ml of toluene and 40 ml of TiCl₄ were used in the reaction steps, and2×100 ml toluene treatments were used after each TiCl₄/toluene reaction.Analysis of the solid catalyst component showed it to contain 19 wt % Mgand 1.6 wt % Ti. Testing was carried out as described in Example 1, andthe results are shown in Table 1, below.

EXAMPLE 5

A solid catalyst component was synthesized following the proceduredescribed in Example 1, except that the reactor was a 250 ml roundbottom flask and 2×100 ml toluene treatments were used after eachTiCl₄/toluene reaction step. Analysis of the solid catalyst componentshowed it to contain 19 wt % Mg and 1.5 wt % Ti. Testing was carried outas described in Example 1, and the results are shown in Table 1, below.

EXAMPLE 6

The procedure described in Example 1 was used to prepare a catalyst,except that the reactor was a 250 ml round bottom flask and one 100 mltoluene treatment was used after each TiCl₄/toluene reaction step.Analysis of the solid catalyst component showed it to contain 17 wt % Mgand 3.0 wt % Ti. Testing was carried out as described in Example 1, andthe results are shown in Table 1, below.

EXAMPLE 7

A catalyst preparation was carried out using the procedure described inExample 3, except that the reactor was a 250 ml round bottom flask and2×100 ml toluene treatments were used after each TiCl₄/toluene reactionstep. Analysis of the solid catalyst component showed it to contain 20wt % Mg and 1.7 wt % Ti. Testing was carried out as described in Example1, and the results are shown in Table 1, below.

EXAMPLE 8

A solid catalyst component was synthesized following the proceduredescribed in Example 3, except that the reactor was a 250 ml roundbottom flask and 1×100 ml toluene treatment was used after eachTiCl₄/toluene reaction step. Analysis of the solid catalyst componentshowed it to contain 17 wt % Mg and 2.9 wt % Ti. Testing was carried outas described in Example 1, and the results are shown in Table 1, below.

EXAMPLE 9

A catalyst preparation was carried out using the procedure described inExample 1, except that 40 ml of toluene and 60 ml of TiCl₄ were used ineach reaction step. Analysis of the solid catalyst component showed itto contain 20 wt % Mg and 1.2 wt % Ti. Testing was carried out asdescribed in Example 1, and the results are shown in Table 1, below.

EXAMPLE 10

A catalyst preparation was carried out using the procedure described inExample 1, except that 60 ml of toluene and 40 ml of TiCl₄ were used ineach reaction step. Analysis of the solid catalyst component showed itto contain 20 wt % Mg and 1.5 wt % Ti. Testing was carried out asdescribed in Example 1, and the results are shown in Table 1, below.

EXAMPLE 11

An aliquot of the catalyst slurry prepared in Example 9 was dried undervacuum. The test procedure described in Example 1 was followed exceptthat the dry catalyst is added to the 45 ml of hexane instead of aslurry. The results are found in Table 1, below.

EXAMPLE 12

A catalyst preparation was carried out using the procedure described inExample 3, except that the reactor was a 250 ml round bottom flask, andthree series of TiCl₄-toluene reactions and 1×100 toluene treatments areused. Analysis of the solid catalyst component showed it to contain 15wt % Mg and 3.8 wt % Ti. Testing was carried out as described in Example1, and the results are shown in Table 1, below.

EXAMPLE 13

A catalyst preparation was carried out using the procedure described inExample 1, except that the reactor was a 250 ml round bottom flask, andthree series of TiCl₄-toluene reactions and 1×100 toluene treatmentswere used.

Analysis of the solid catalyst component showed it to contain 15 wt % Mgand 3.8 wt % Ti. Testing was carried out as described in Example 1, andthe results are shown in Table 1, below.

EXAMPLE 14

In this Example, 5.0 g of a mixed phase ClMg(OEt) was charged into a 250ml 4-neck round bottom flask as described in Example 1. Then, 30 ml oftoluene was added, the mixture was stirred to suspend the solid, 20 mlof TiCl₄ was added to the stirred slurry, the slurry was heated to 90°C., and 1.95 g of di-isobutylphthalate was added. The mixture was heatedto 115° C. and was held at this temperature for two hours.

Following the procedure in Example 1, the supernatant was decanted, andtwo treatments with 100 ml of toluene each were carried out. TheTiCl₄+toluene reaction/toluene treatment step were repeated threeadditional times. The solids were then washed four times with 100 mlheptane each time. An additional 100 ml of heptane was added to theflask, the slurry was transferred to a vacuum filter apparatus, filteredand dried.

Analysis of the solid catalyst component showed it to contain 21 wt % Mgand 1.3 wt % Ti. Testing was carried out as described in Example 1,except that the dry catalyst was added to the 45 ml of hexane instead ofa slurry. The results are shown in Table 1, below.

EXAMPLE 15

A slurry of a solid catalyst component was prepared in then same manneras Example 14 with the exception that the di-isobutylphthalate was addedat room temperature after the addition of the initial TiCl₄ charge.Analysis of the solid catalyst component showed it to contain 20 wt % Mgand 1.4 wt % Ti. Polymerization testing results, obtained under the sameconditions as shown in Example 1, are found in Table 1, below.

EXAMPLE 16

A portion of the catalyst slurry obtained in Example 15 was filtered andvacuum dried. Table 1 contains the polymerization test results for thiscatalyst, carried out under the conditions of Example 1, modified forthe use of dry catalyst as in Example 11. The results of this Exampleare not illustrated in Table 1.

EXAMPLE 17

The catalyst prepared in Example 1 was tested for polymerizationperformance as in Example 1, except that the test is run at 80° C. forone hour. The averaged results of two tests were as follows: activity,132.6 kg/g catalyst; poured bulk density, 0.474 g/ml; total xyleneinsolubles, 99.37 wt %.

COMPARATIVE EXAMPLE 1

The procedure described in Example 12 was followed to produce a solidcatalyst component except that 1.43 g of phthaloyl dichloride wassubstituted for diisobutylphthalate. The results of polymerizationtesting using the procedure in Example 1, modified for the use of drycatalyst as in Example 11, are presented in Table 1, below.

COMPARATIVE EXAMPLE 2

A catalyst preparation was carried out using the procedure described inExample 1, except that 40 ml of toluene and 10 ml of TiCl₄ were used inthe reaction steps. Analysis of the solid catalyst component showed itto contain 22 wt % Mg and 0.69 wt % Ti. Testing was carried out asdescribed in Example 1, and the results are shown in Table 1, below.

TABLE 1 Catalyst Performance Results yield # Tests time of kg/g PBD TXIExample # averaged run, hr cat g/ml wt %  1 3 1 85.5 0.468 98.82  1 1 2120.6 0.473 98.93  2 2 1 74.3 0.458 98.96  3 2 1 76.4 0.479 98.86  4 2 166.9 0.487 98.95  5 2 1 80.9 0.472 98.96  6 2 1 77.5 0.467 98.99  7 3 169.1 0.483 98.96  8 3 1 69.5 0.470 98.88  9 3 1 69.1 0.470 99.03  9 1 2100.2 0.478 98.95 10 2 1 60.7 0.453 98.78 11 2 1 46.3 0.410 98.88 12 2 153.5 0.472 98.49 13 2 1 65.0 0.457 99.00 14 3 1 48.6 0.428 99.04 15 1 187.9 0.424 98.80 16 2 1 66.0 0.359 98.67 Comp. 1 1 1 20.7 0.460 99.33Comp. 2 2 1 35.9 0.407 99.37

EXAMPLE 18

In this Example, 5.0 g of a pure phase ClMg(OEt), as described in U.S.Pat. No. 5,262,573, was slurried with 30 ml of toluene and 20 ml ofTiCl₄. The slurry was heated to 90° C. and 1.94 g of diisobutylphthalatewas added. The remainder of the process was then carried out asdescribed in Example 1, using 100 ml of toluene for the treatment stepsand 30 ml of toluene and 20 ml of TiCl₄ for the reaction steps. Theproduct was washed with heptane and isolated by vacuum drying.

Testing was carried out as described in Example 1, and the results areshown in the following Table:

# Tests time of yield PBD TXI averaged run, hr kg/g cat g/ml wt % 3 168.5 0.386 98.62

The foregoing Examples illustrate the following features and performancecharacteristics of the catalyst. Examples 1-8 describe modes forpreparing the catalyst along with the effects of varying theTiCl₄/toluene ratio and number and volume of toluene treatments. Example1 versus Example 9, and Example 3 and 7 versus Example 10 show thebenefit of reducing the volume of the TiCl₄/toluene reaction mixturefrom 10 ml/g support precursor (Examples 9 and 10) to 5 ml/g supportprecursor (Examples 1, 3, and 7).

Example 9 versus Example 11 illustrates the improvement in catalystperformance when the catalyst is not dried and is isolated as a slurryversus isolation as a dry powder. Example 3 versus 12 and Example 6versus 13 exhibit the difference found for carrying out four versusthree treatment cycles. Example 9 versus Example 15 compares the effectsof the temperature of addition of the diisobutylphthalate (DIBP)internal donor, 70° C. versus room temperature, for catalysts isolatedas slurries (room temperature, higher activity).

Examples 14, 11, and 16 show the effect of the temperature of additionof the DIBP internal donor, 90° C. versus 70° C. versus roomtemperature, for catalysts isolated as dry powders (room temperature,higher activity).

Example 17 shows the increase in activity achieved when thepolymerization test is run at 80° C. instead of 70° C.

Example 18, which is best compared to Example 11 that used a mixed phaseClMg(OEt) support precursor, shows the present invention using, as astarting reagent, a pure phase ClMg(OEt) material. The activity of thecatalyst was almost 50% greater than that for the mixed phase supportmaterial.

Example 14 versus Comparative Example 1 shows the use of a phthalateester, DIBP in this case, gives a superior catalyst to the use of thecorresponding acid chloride, phthaloyl dichloride, when ClMg(OEt) is thesupport precursor (dry catalyst).

Comparative Example 2 versus Examples 1-4, shows that reducing thevolume % of TiCl₄ in the TiCl₄/toluene reaction mixture from 40% to 20%causes a large loss in activity, not evident from the trend found in the80%-40% range.

The foregoing Examples, since they are being provided to merelyillustrate certain embodiments of the present invention, should not beconstrued in a limiting fashion. The scope of protection sought is setforth in the claims that follow.

1. A process for forming a propylene polymerization catalyst whichcomprises: forming a combination of titanium tetrachloride, amagnesium-containing compound that can be converted to magnesiumdihalide and an internal electron donor in an aromatic hydrocarbonsolvent, with the proviso that, the magnesium-containing compound cannotbe a magnesium dialkoxide when the internal donor is a halo phthaloylderivative, and bringing that combination, as modified by the provisoclause, to elevated temperature to form an intermediate product; washingthe intermediate product with an aromatic hydrocarbon solvent atelevated temperature to produce a washed product and a supernatantfollowed by decantation of the supernatant therefrom; treating thewashed product with titanium tetrachloride in an aromatic hydrocarbonsolvent to form a treated product and a supernatant followed by heatingof the treated product and supernatant, decantation of the supernatanttherefrom, and washing of the treated product with an aromatichydrocarbon solvent at elevated temperature to produce a washed productand a supernatant followed by decantation of the supernatant therefrom;treating the washed product with titanium tetrachloride in an aromatichydrocarbon solvent at least one more time, to form a treated productand a supernatant followed by heating of the treated product andsupernatant, decantation of the supernatant therefrom, and washing ofthe treated product with an aromatic hydrocarbon solvent at elevatedtemperature to produce a washed product and a supernatant followed bydecantation of the supernatant therefrom; and addition of an aliphatichydrocarbon solvent to the washed treated product with decantation ofthe solvent therefrom to form a doubly washed product which can be usedas a propylene polymerization catalyst.
 2. A process as claimed in claim1, further comprising: after the formation of the doubly washed productresulting from addition of the aliphatic hydrocarbon solvent, and addingmineral oil to the doubly washed product to form a slurry containing thepropylene polymerization catalyst.
 3. A process as claimed in claim 1wherein the aromatic hydrocarbon solvent employed in the severalwashings is an alkylbenzene solvent.
 4. A process as claimed in claim 1wherein the magnesium-containing compound that can be converted tomagnesium dihalide is a magnesium chloroalkoxide that contains up toabout twelve carbon atoms in its alkyl moiety.
 5. A process as claimedin claim 1 wherein the internal electron donor is a phthalate ester thatcontains up to about twelve carbon atoms in its alkyl groups.
 6. Aprocess as claimed in claim 4 wherein the aromatic hydrocarbon solventis toluene and the magnesium chloroalkoxide is magnesium chloroethoxide.7. A process as claimed in claim 2 wherein the aliphatic solvent ishexane.
 8. A process as claimed in claim 4 wherein the magnesiumchloroalkoxide contains four carbon atoms in its alkyl moiety.
 9. Aprocess as claimed in claim 5 wherein the phthalate ester isdiisobutylphthalate.
 10. A process as claimed in claim 1 wherein thearomatic hydrocarbon solvent is toluene, the magnesium-containingcompound that can be converted to magnesium dihalide is a magnesiumchloroalkoxide, and the internal electron donor is a phthalate esterthat contains up to about twelve carbon atoms in its alkyl groups.